1. Field of the Invention
The present invention generally relates to a liquid crystal display device and, more particularly, to a technique to connect a circuit board to a liquid crystal panel of a liquid crystal display device.
2. Description of the Related Art
A conventional liquid crystal display device comprises a liquid crystal panel and a plurality of drive integrated-circuits (drive ICs) for driving the liquid crystal panel. FIG. 1 is a plan view of a conventional liquid crystal display device.
The liquid crystal display device shown in FIG. 1 comprises a liquid crystal panel 2, a plurality of source-side drive ICs 4-1 and a plurality of gate-side drive ICs 4-2. Liquid crystal display signals are supplied from an external circuit (not shown in the figure) to the source-side drive ICs 4-1 and the gate-side drive ICs 4-2 via an input board, circuit boards 8 and 10, a connection board 11 and flexible boards 12 and 14. The liquid crystal display signals are converted into drive signals by the source-side drive ICs 4-1 and the gate-side drive ICs 4-2, and the drive signals are supplied to the liquid crystal panel 2 via the source-side flexible boards 12 and the gate-side flexible boards 14.
Generally, a TCP is used for each of the source-side flexible boards 12 and the gate-side flexible boards 14. FIG. 2 is a plan view of one of the source-side flexible boards 12 and the gate-side flexible boards 14, viewed from a side of a circuit pattern formation surface. FIG. 3 is a cross-sectional view of one of the source-side flexible boards 12 and the gate-side flexible boards 14. As shown in FIG. 3, each of the flexible boards 12 and 14 has a copper foil 20 attached to a base film 16 via an adhesive 18. The copper foil 20 is formed in a predetermined pattern. The base film 16 has an opening 16a at a position to mount the source-side drive IC 4-1 or the gate-side drive IC 4-2. A seal resin 22 is filled in the opening 16a. 
As shown in FIG. 2, the flexible boards 12 and 14 are provided with input signal lines 12a and 14a and output signal lines 12b and 14b, respectively. The input signal lines 12a and 14a supply input signals to the drive ICs 4-1 and 4-2, respectively, and the output signal lines 12b and 14b supply output signals of the drive ICs 4-1 and 4-2 to the liquid crystal panel 2.
In the connection method of the signal lines shown in FIG. 1, signal-line connection is required at two positions, one of which is the connection between the liquid crystal panel 2 and each of the flexible boards 12 and 14 and the other is the connection between the flexible boards 12 and 14 and the respective circuit boards 8 and 10. The circuit boards 8 and 10 are provided for merely supplying the input signals to each drive IC. Thus, if the circuit boards 8 and 10 are eliminated from the liquid crystal display device, a manufacturing cost of the circuit boards 8 and 10 is eliminated and also a process for connecting the circuit boards 8 and 10 is eliminated.
Thus, there is suggested a method of eliminating the gate-side circuit board 10 by providing input wiring terminals (or through terminals) on the gate-side drive IC 4-2 as shown in FIG. 4. Specifically, the gate-side drive IC 4-2 shown in FIG. 4 is provided with the input wiring terminals from which the input signals are output without any change. In FIG. 4, terminals A, B, C, D and E are input terminals, and terminals A′, B′, C′ and D′ are the input wiring terminals from which the input signals supplied to the input terminals are output without any change. By preparing a drive IC having the above-mentioned structure, the input signals (liquid crystal display signals) can be supplied to each drive IC 4-2 via the flexible board 14 and the liquid crystal panel 2. That is, as shown in FIG. 5, the input signals can be supplied to the gate-side drive ICs 4-2 sequentially one after another by forming input signal lines 2a on the liquid crystal panel 2. Thereby, the gate-side circuit board 10 can be eliminated.
If the source side has a structure that is the same as that of the above-mentioned structure of the gate side, the source-side circuit board 8 can also be eliminated. However, the signal lines of the source side must be smaller than that of the signal lines of the gate side. Generally, when forming the input signal lines 2a on the liquid crystal panel 2, a conductive layer is formed on the liquid crystal panel 2 by a film deposition process or the like, and the conductive pattern is patterned so as to form signal lines. Accordingly, the thickness of the wiring pattern formed on the liquid crystal panel 2 cannot be as large as a thickness of signal lines formed on a flexible board which is formed by patterning a copper foil attached to a flexible base board. Thus, there is a problem in that it is difficult to form a signal line having a low wiring resistance. Accordingly, as shown in FIG. 5, the source-side circuit boards 8 remain unchanged, and only the gate-side circuit boards 10 are eliminated.
Additionally, since a generally used drive IC does not have the input wiring terminals shown in FIG. 4, the drive IC shown in FIG. 4 must be newly designed and manufactured. Thus, the development of such a new drive IC having input wiring terminals requires extensive time and cost.